There are numerous uses for solenoids that have a plunger which may be held in either of two end positions while being selectively movable between those positions by pulsed energization of an electromagnetic coil. Uses of such devices include holding, locking, or latching another device in a predetermined position, subject to release upon appropriate energization of a coil in the solenoid. All such uses are sometimes referred to hereinafter as "latching." One particular example is the use of a latching solenoid to lock the cover of a computer device in a closed position.
A typical magnetic latching solenoid basically comprises a conventional electrical coil operated solenoid with a permanent magnet in the structure. The permanent magnet provides a permanent magnetic attraction force for retaining a solenoid armature, sometimes referred to as a "plunger," in either of two end positions. The electric coil is used to generate a momentary pulse of a magnetic field to momentarily overcome the magnetic attraction field of the permanent magnet and to drive the plunger to change its position. The resulting movement of the plunger will drive a push rod that may be used to perform a locking operation. The same coil or another coil then may be energized momentarily in an opposite sense to release and move the plunger in the opposite direction for unlocking purposes, such as by using an electrical pulse generating device that is activated only upon entry of an appropriate code on a related keyboard. Latching solenoids are used in great numbers for such operations. It is desirable to provide solenoids which will operate reliably for such uses and which can be produced in a facile manner at low costs.